Normally, a flange portion is projected on a wheel rolling bearing apparatus for supporting a wheel of a motor vehicle for fixedly attaching the rolling bearing apparatus to a suspension system on the vehicle side. This flange portion includes a first flange portion which is projected on an upper side of an outer circumferential surface of an outer race member and a second flange portion which is projected on a lower side thereof, and the first flange portion and the second flange portion each include a plurality of projecting flange portions. A bolt hole is formed in each flange portion so as to extend in an axial direction, and a female thread is formed in an inner circumferential surface of the bolt hole so as to enable a bolt to be screwed into the bolt hole to thereby fasten the flange portion to the suspension system (for example, refer to Patent Document 1).
Since a moment load is applied to the rolling bearing apparatus as the vehicle turns, for example, when the vehicle turns to the right, strong tensile stress is generated in the first flange portions of the rolling bearing apparatus disposed particularly in a left wheel of the vehicle. Because of this, a proximal end portion of a surface of the first flange portion which faces the outside of the vehicle is smoothly connected to the outer circumferential surface of the outer race member by a reinforcement portion so as to restrain the flange portion from being inclined with respect to an axis of the outer race member. An upper surface of the reinforcement portion which connects the flange portion with the outer circumferential surface of the outer race member constitutes an arc-shaped concave curve in an axial section of the outer race member. Namely, the reinforcement portion connects smoothly the flange portion with the outer circumferential surface of the outer race member by an arc-shaped concavely curved surface.
In addition, since compression stress is generated in a proximal end portion of the second flange portion as the vehicle turns, a reinforcement portion is also projected on a proximal end portion of a surface of the second flange portion which faces the outside of the vehicle to thereby connect the proximal end portion with the outer circumferential surface of the outer race member by an arc-shaped concavely curved surface.
The first flange portions and the second flange portions are all formed into the same shape, and the reinforcement portions are all also formed into the same shape.